I wanted to post another WIP of my process, if it might help someone in the community. So I chose my Thanos painting to illustrate the subject, though I didn't push this piece on a high level of detail. The main purpose is to show the steps of building up a painting.
It is the process I chose for this painting, there are hundreds of different ways to do it, and I don't intend to teach anyone how to draw or paint, because I still consider myself as a student. But I'll be happy if it can help someone improve their art

Last thing : I use PS cs3